Within the field of neurotechnology, deep brain stimulation (DBS) is a surgical treatment involving the implantation of a medical device called a deep-brain stimulator, which sends electrical impulses to specific parts of the brain. DBS in certain brain regions has provided remarkable therapeutic benefits for otherwise treatment-resistant disorders such as chronic pain, Parkinson's disease, tremor and dystonia. Despite the long history of DBS, its underlying principles and mechanisms are still not clear. DBS directly changes brain activity in a controlled manner. Unlike lesioning techniques, its effects are reversible. Furthermore, DBS is one of only a few neurosurgical methods that allow blinded studies.
FIG. 1 illustrates an example of a DBS system 10 according to prior art. In principle, the DBS system comprises two components, illustrated by FIG. 1: the implanted pulse generator (IPG) 11, and the probe 12. The IPG 11 is a battery-powered neurostimulator that sends electrical pulses to the brain to interfere with neural activity at the target site. The IPG 11 is typically encased in e.g. a titanium housing. The probe 12 consists of about 10-15 cm long wires and a plurality of electrodes. The wires connect the IPG to the electrodes 13, which are located at the distal end of the probe. The IPG may be calibrated by a neurologist, nurse or trained technician to optimize symptom suppression and control side effects.
DBS probes are placed in the brain according to the type of symptoms to be addressed. All components are surgically implanted inside the body. The typical procedure is performed under local anesthesia, where a hole is drilled in the skull and the electrode is inserted with feedback from the patient for optimal placement. The right side of the brain is stimulated to address symptoms on the left side of the body and vice versa. FIG. 2 is illustrating how a DBS system 10 may be positioned in the brain of a person 21. FIG. 3 illustrates how two DBS systems 10 may be positioned in the brain of a person 31, to stimulate both left and right side of the body of person 31.
When a person with a DBS probe undergoes an examination with magnetic resonance imaging (MRI), a strong electric field may result near the end of the probe as a result of the electromagnetic field coinciding with the probe. This electric field induces currents that heat up the brain tissue. Excessive heating may destroy the brain tissue. For example, it has been shown that for an insulated, 20 cm long straight wire, the temperature in surrounding tissue may increase to 48° C. in the normal operating mode of an 1.5 T MRI system. In contrast, only temperature increases less than 1° C. are considered safe.
In order to resolve the problem of induced currents and thus undesired heating of human tissue, high impedance probes have been suggested. Simulations indicate that the overall impedance of a probe should be at least 1 kΩ for the current to be sufficiently low, consistent with Ohm's law.
However, such high impedance leads to a very limited battery life. By configuring a probe with a number of parallel electrically conducting leads, having a spiral form, the battery life may be increased, since the overall impedance of such a probe is the sum of the impedance of all the interconnect leads, e.g. electrical conducting wires in parallel. For instance, the overall impedance of 50 parallel leads with individual impedance of 1 kΩ is 20Ω.
FIG. 4 is showing an internal view of the probe 12 according to prior art, wherein a number of electrically conducting leads 41 run from a first end 42 of said probe to electrodes 13, which are located at the distal end of the probe. In use, the probe 40 is connected at the first end 42 to a power source and electronics, such as an IPG, enabling an electric current to flow through said electrically conducting leads 41 to the electrodes 13.
However, due to the spiraling form of the electrically conducting leads 41, high voltages and/or currents are resulting in the electrically conducting leads, when the probe is subjected to an external magnetic field, such as when performing MRI. Thus, there is a risk that the electronics of the IPG, connected to the electrically conducting leads 41, is damaged when the spiraled conducting leads 41 are subjected to an external magnetic field.
Hence, an improved DBS probe allowing for increased flexibility, cost-effectiveness, sufficiently long battery life, safe operation of electronics and prevention of excessive heating of tissue during MRI examination would be advantageous.